Various types of catalysts are known and used in a variety of applications. For example, catalysts may be fused, supported or unsupported and used in applications such as for example purifying exhaust gases. Supported catalysts are typically composed of a catalyst support, active catalytic ingredients provided on the catalyst support and promoters/additives. The catalyst support provides a surface to disperse the active catalytic ingredients, a surface area for contact with reactants, mechanical support for the active catalytic ingredients and a surface to disperse reaction heat around the active catalytic ingredients. The active catalytic ingredient may be selected from metal, metal oxides, metal sulphides and combinations thereof. Promoters and additives are included to modify the properties of the active catalytic ingredients. These properties include, for example, increasing the acidity or basicity of active metal ingredients, creation of special sites for enhancement of catalyst activity and selectivity and increasing the mechanical and thermal properties of the catalyst system.
Catalysts in general have been traditionally produced using conventional techniques of precipitation, co-precipitation, impregnation, co-impregnation, ion-exchange and deposition-precipitation processes that are well known to those skilled in the art. In the case of supported catalysts, these have been typically produced using multi-stage processes which are complicated, expensive, time consuming and often involve unknown complex chemistry and procedures. The variables involved in such multi-stage processes must be carefully monitored and controlled in order to preclude large quality variations of the resultant supported catalysts from lot to lot.
As will be appreciated, catalyst performance depends on a number of catalyst properties. These properties include the dispersion of active catalytic ingredients on the catalyst support, the surface area and pore structure of the catalyst support, the presence of active catalytic sites, and the nature of the catalyst support (acidic or basic catalytic sites). The dispersion of active catalytic ingredients on the catalyst support strongly influences the interaction of the supported catalyst with the process materials stream. Good dispersion combined with the presence of properly oriented active catalytic ingredients sites drives the catalytic reaction to chemical equilibrium faster.
Any small amount of impurities present in the active catalytic ingredients can strongly influence the catalyst performance in a negative manner thus diminishing the effectiveness of the catalyst and its catalytic activity in general.
In a completely unrelated field, hydrometallurgical processes have typically been used in the cladding of core materials with metals, metal oxides, metal sulphides, etc. The most common practical application of this technology relates to cladding of core materials with metals. Hydrometallurgical processes generally involve cladding of a core material having a low specific surface area. For example, graphite cores with an average particle size of about 100 μm are used in the production of nickel clad graphite for electronic shielding applications. These cores have a specific surface area of approximately 0.1 m2/g. In another example, nickel powder of about 20 μm in size is used in the production of nickel clad alumina for hardfacing and has a specific surface area of approximately 0.15 m2/g. For these applications, a thick coating of a deposited metal is generally desirable. In the above-mentioned nickel clad alumina example, it is desirable to coat alumina with a thick layer of several micrometers of nickel for increased wear resistance and ductility in the final product. A cross section of a typical composite particle produced by conventional hydrometallurgical processes includes a core material with low surface area and a thick coating of metal on the particle surface.
Conventional hydrometallurgical processes are used in cladding for purposes such as wear resistance in the case of nickel cladding of alumina and electrical conductivity in the case of nickel cladding of graphite. However, such hydrometallurgical processes have not been contemplated nor developed for the production of catalysts especially supported catalysts where providing a highly active catalytic surface is desired and required. This is because these processes are not satisfactory for the production of catalysts, particularly supported catalysts.
It is therefore an object of an aspect of the present invention to provide a process for the production of a supported catalyst that obviates or mitigates at least some of the disadvantages of the prior art processes. It is further desirable to provide novel and improved supported catalysts.